In traditional white- and rosé-wine vinification, thermovinification of red wine, as well as other more specific types of vinification, the must-cleansing process, known as clarification, is a key step in obtaining quality wines.
The presence of deposits or impurities in the must obtained after pressing the fruit leads to problems in the subsequent processes, such as fermentation in the case of grapes. These impurities, besides producing undesirable vegetable aromas, cause the yeast to precipitate, leaving its sediment on the bottom of the fermentation vat, which adversely affects the vinification process.
Clarification of the must can be carried out using various methods: the static method, the centrifugation method, the vacuum rotary-filtration method, and floating.
Static clarification simply comprises natural sedimentation or with the help of must-clarificating products, thus removing the deposits and colloids contained in the must at the bottom of the vat. It is a batch process lasting between 8 and 48 hours and which requires a large amount of energy to keep the must cool in order to accelerate sedimentation, and prevent fermentation from starting.
Clarification using the centrifugation method is a batch process that comprises the removal of deposits from the must by physical separation as a result of centrifugal force applied inside a special machine. It is a process that can be made continuous by incorporating the number of spinners necessary so that while some are working, others are being cleaned, and others are being loaded, the resulting flow therefore being more or less continuous. It is a process that is aggressive with the must, and recommended to process very large volumes of must that do not need to be of high quality.
Clarification by vacuum rotary filtration is a batch process that consists of passing the must, aided by a vacuum force, through a filter composed of a succession of filter-material layers, which is usually of a clayey nature. This is a slow process that is aggressive with the must, particularly recommended to take advantage of deposits neglected by other methods, or musts that are very difficult to clarify or of very low quality.
Finally, we come to the clarification by floating. This is a continuous or batch process that consists of injecting air into the must so that the deposits or impurities contained in it float to the surface of the flotation vat, so that the clean must can be extracted from the bottom. It is a process that is not very aggressive with the must and is recommended for processing large quantities of must. The air is generally forced in by a compressor unit, through injectors located in the base of the flotation vat. Apart from the increase in power consumption implied by this compressor unit, the air injection is produced locally in the application points, and the clarification is therefore not homogeneous.
In the state of the art, European patent no. EP0838260 is known, which describes an apparatus for the aeration and pumping of loaded liquids applicable to the winemaking sector, which includes a motor provided with a vertical shaft with a helical coil. The drawback of this apparatus is that the aeration is produced in a very localised manner in the application point, that is, in the vicinity of the helical coil, not ensuring the aeration to the most distant points.